1. Field
The present invention relates to wireless communications and, more particularly, relates to discovery and association in a wireless network that includes devices with asymmetric antenna systems.
2. Description of the Related Technology
A wireless communication network is commonly associated with a telecommunications network where the interconnections among the devices of the network are implemented without the use of wires. Such networks are generally implemented with some type of remote information transmission system that uses electromagnetic waves, such as radio waves, for the carrier.
A wireless personal area network (WPAN) is one type of wireless network used for communication among a plurality of devices, such as computers, mobile phones, personal digital assistants, printers, digital cameras, televisions, media players, etc. Usually, a WPAN covers a short range of up to 10 or 20 meters. A number of standards for such short-range network communications have recently been developed, including Bluetooth and IEEE 802.15, for example.
Some embodiments of a WPAN operate at high frequencies, e.g. about 60 GHz, at which free space path loss is higher than at lower frequencies due to the fact that free space path loss increases quadratically with frequency. To compensate for such high attenuation, some network devices are configured to transmit directionally, in which the received signal is stronger at particular locations as compared to other locations. To achieve this, some network devices employ sector antennas which physically direct the radiation pattern of the antenna in a particular direction. Other methods of direction transmission include beamforming, in which many antennas transmit weighted versions of the same signal resulting in some locations in which the many transmissions are in-phase and add together to result in strong reception and other locations in which the many transmissions are out-of-phase and result in weaker reception.
Some network devices employing directional transmission also employ directional reception. In some embodiments, the same antennas are used for reception and transmission, resulting in a symmetric antenna system (SAS), in which the transmission directions and reception directions are the same. In other embodiments, different antennas are used for reception and transmission, resulting in an asymmetric antenna system (AAS), in which the transmission directions and reception directions are different. A device with only one set of antennas used for both reception and transmission can still include an asymmetric antenna system (AAS) if the transmission directions and reception directions are different.